The invention relates to a radial shaft sealing ring as recited in the preamble of claim 1.
When radial shaft sealing rings of the kind in question are mounted their sealing lip which is oriented radially inwardly in unassembled condition is bent elastically in axial direction so that its free end will enter into axial engagement with the surface of the shaft (cf. SAE Technical Paper 930531 xe2x80x9cAdvanced Analytical Techniques of the Optimization of PTFE Sealsxe2x80x9d, D. M. Toth, R. Hatch, G. Upper). Measurements and calculations have revealed that the place of maximum contact pressure of the sealing lip against the shaft surface is shifted towards the side of the air and that there is practically no contact pressure acting on the free end of the sealing lip. As a result, the sealing lip may lift off, especially when there is excessive pressure in the space to be sealed. This phenomenon is referred to in the art as xe2x80x9cbell mouthingxe2x80x9d.
DE 33 27 229 A1 discloses a radial shaft sealing ring of the kind mentioned initially of which the sealing lip is partly split by circular, continuous ring cuts so as to enhance its flexibility.
It is the object of the invention to design a radial shaft sealing ring of the kind defined in the preamble of claim 1 such that contact pressure of the sealing ring throughout the entire area in engagement with the surface is securely warranted even when high pressure exists in the space to be sealed.
This object is met by a shaft seal as defined in claim 1 and a method of making the same as defined in claim 13.
The contact pressure means of the present invention which preferably does not touch the shaft and, if so, engages it without exerting a force thereon, keeps the sealing lip, preferably the free end thereof constantly pressed against the surface of the shaft by subjecting it to a force with a radially inwardly directed component. In this manner the undesirable xe2x80x9cbell mouthingxe2x80x9d and thus the risk of leakage are avoided. That is true in particular also in cases of application where the pressure in the sealed space, is higher than the pressure at the so-called air side, namely ambient pressure, for example atmospheric pressure.
The contact pressure means preferably is an elastic contact pressure lip which is integral with the sealing member and formed by radial slitting or splitting. It exerts the pressure mentioned on the free end of the portion of the sealing lip. Due to its manufacture, this contact pressure lip, before being mounted, preferably has the same inner diameter as the sealing lip. Upon assembly, the contact pressure lip automatically adjusts itself so that it will contact the sealing lip only at the free end thereof and will not touch the shaft.
Further advantageous embodiments of the invention are covered by the subclaims. It is known to provide the surface area of the sealing lip, especially where it engages the shaft with feedback structures embodied, for example, by spiral grooves (SAE Technical Paper 930531, FIG. 1, see above). Such grooves are open towards the space to be sealed so as to be able to return any medium which enters the sealing gap back into the space to be sealed. When there is excess pressure in the space to be sealed it may happen that medium to be kept sealed off is pressed in opposite direction through the groove or grooves thus penetrating the sealing gap and leaking from the sealed space into the surroundings.
To prevent that from happening, it is provided in a further development of the invention which is important also in itself that the feedback structure is closed towards the medium side and/or the air side.